Radio receiver



March 16, 1943. M, HOBBS I RADIO RECEIVER Filed Feb. 2, 1942 All bhw

kwww

INVENT OR. NA lPV/N HOBBS ATTORNEYS Mai-ch 16, 1943.

M. HOBBS RADIO RECEIVER Filed Feb. 2, 1942 3 Sheets-Sheet 2 I INVENTOK MARVIN HOBBS ATTORNEYS March 16, 1943. M. HOBBS RADIO RECEIVER 5 Sheets-Sheet -3 Filed Feb 2, 1942 INVENTOR. NA 2e w/v HOBBS BY Q W iatented Mar. 16, 1943 UNITED ST RADIO RECEIVER Marvin Hobbs, Chicago, 111., assignor to E. B. Scott Appiication February 2, 1942, Serial No. 429,275

10 Claims.

This invention relates to improvements in receiving systems for radio signals and more particularly to improvements in the method and apparatus of preventing undesirable radiations from the receiver.

As is well known, the so-called super-heterodyne types of receivers include in their combination a local oscillator, the purpose of which is to generate a local signal, which signal is mixed with the incoming signal to provide a heterodyne or beat signal that is the difference between local and received signals, whichbeat signal is amplified, detected, and eventually reproduced audibly.

Heretofore the radiation of the oscillator signal from the receiver was thought to have been substantially eliminated due to the fact that one or two vacuum tubes were interposed between the oscillator tube and the antenna circuit of the receiver. This, together with conventional shielding, was believed to be sufiicient to prevent the radiation from being troublesome. Preselection was also thought to be the answer to preventing this radiation. As a matter of fact, the radiation of the oscillator was ignored inasmuch as it was not very strong and was considered to be a necessary evil. It was believed that it was suppressed as much as was possible, and since this rather weak signal very often did not fall in the broadcast band and did not cause serious interference with broadcast receivers, it was not considered important. Furthermore, it was of such low strength that the desired signals very often over-rode the interfering signal and it was unnoticed.

However, in the case of receiver operation in crowded apartment districts, several receivers may be coupled to the same antenna either directly or through some form of antenna current distribution system. In these events it has been found that in spite of the use of pre-selection in the various receivers there was still undesirable interference. Furthermore, as the frequency was raised, the interference usually became stronger. This was particularly true in connection with operations on the short wave bands. For in stance, in a specific case a receiver covering a range from 5.5 to 9.5 mo. (megacycles) was found to put out a signal of 20 m.v. (microvolts) at 55 mo. and 500 m.v. at 9.5 me. at the antenna terminals; and in the range from 9.6 m.c. to 15.6

m.c. there was found to be a raise from 20 m.v. to

When a proper antenna match was provided for the receiver it was found that the receiver radiated quite efficiently and could be heard over considerable distance.

It becomes very desirable to limit this radiation under certain circumstances. This is particularly true for receivers which are used in marine communication for here the receiver is usually picking up signals that are weak and therefore the sensitivity of the receiver has to be greater than in the ordinary receiver such as is encounsignal or cause such interference as to prevent the desired reception in the other receiver. This might result in very serious consequences. In the case of marine reception it might be necessary that both of these signals be received and noted in the furtherance of life and security, and to say the least, this interference would be very annoying.

Still another and extremely important undesirable effect is apparent in times of war. A ship carry valuable cargo, or personnel and under orders to maintain strict radio silence, even though its transmitters are shut down, becomes a potential broadcast station sending out signals from their receivers that may be picked up and used by enemy craft to guide them directly to their objective.

Therefore, it is one of the primary objects of this invention to provide a radio receiver wherein radiations of the receiver oscillator signal or other signals arising within the receiver are substantially, if not completely, eleminated.

Another object of the invention is the provision of an improved mechanical and electrical shielding structure in a receiver such that unwanted signals are eliminated.

Still another object of the invention and the invention itself becomes more apparent from the following description of an embodiment thereof, whichis illustratedby the accompanying drawings and forms a part of this specification.

In the drawings:

Fig. 1 is a diagrammatic view of the antenna, radio frequency and oscillator compartments of a radio receiver having included therein an embodiment of the invention;

Fig. 2 is a sectional view through a receiver chass s illustrating certain structural features of my invention;

Fig. 3 is a top plan view thereof;

Fig. l is a bottom plan view thereof, only such parts being shown as are peculiarly applicable to the invention; and

Fig. is a simplified circuit diagram of the radio frequency, oscillator and mixer stages of a receiver circuit embodying my invention.

Referring to the drawings throughout which like parts have been designated by like reference characters, and particularly to Figs. 2-4, there is provided a chassis base I which, generally speaking, is of standard metal construction including a top, sides, ends and a removable bottom plate. In ordinary construction it is common practice to mount the tubes on top of the base and the majority of the wiring is concealed below the base. Also the intermediate frequency transformers etc. are usually placed on the top of the base. Inasmuch as the invention herein has to do particularly with the radio frequency, mixerand oscillator stages .only, these stages only are shown; it will be understood, however, that the invention is parti la ly useful in connection with theother components of a complete receiver. In the present invention the inductances .and capacitances for tuning the inductances are disposed in a separate container 2, which container is supported in an opening '3 in the base with part of the container extending above the top of the base and the remainder below the top of the base. The container is provided with Leshapf d lugs .4 which support the container on the .base upon suitable insulating grommets. The container is grounded to the chassisbase at one point as indicated at 6.

The mixer and oscillator stages are disposed in a larger container ,8 supported in ,an opening i in a similarmanner. This container is grounded to the chassis .at 10.

The containers 2 and .8 also have disposed therein tuning condensers H and .12 (Fig. 3.) which operate .in the well known manner, the condenser II in the container 2 being for tuning the antenna circuit, and those in the container 8 for tuning the oscillator and radio frequency circuits. All of the variable condensers are rotated simultaneously by a single shaft 14. The antenna circuit tuning condenser is, however, isolated from the .others by the insulated coupling I5 which provides an electrical break in the shaft.

The antenna compartment 2 (Fig. 1) is provided exteriorly with connections for an antenna and ground. The antenna connections may be for a doublet, although the invention is by no means limited to any particular type of antenna circuit. This compartment 2 contains the various inductances as Well as variable condensers for tuning the same. These components may be conventional if desired.

As is common practice, the antenna coupling coils may be connected into the input circuit of a vacuum tube device (Fig. 5), the connection being to the grid circuit through the grid cap. In this connection with a view to complete isolation of the antenna circuit from the remainder of the circuit, a 6K7 tube of the metal type may be employed. This tube (Fig. 1) is supported in the usual socket l5 which, however, in this instance is disposed inside of the radio frequency and oscillator compartment 8. The body .of the tube extends through an opening I? in the container and over through an opening 45 .of the antenna compartment 2 into the antenna compartment where the grid cap is connected to the antenna circuit in any convenient manner. This tube which is known as the first radio frequency tube thus bridges the gap between the two separate compartments and the signal from the antenna circuit is conducted through the tube in the usual manner to the remainder of the circuit. See Fig. 5.

The other compartment 8 contains the mixer (or as is sometimes called the first detector) circuit and the oscillator circuit. The tubes in the circuit are supported in the usual manner on a base l8 (Fig. 1) which divides this compartment into upper and lower spaces.

The mixer and oscillator circuit may also be conventional and comprise the usual inductances and capacitances for tuning to the incoming signal and providing the proper local oscillator signal which is fed into the mixer to provide the usual heterodyne signal that is subsequently amplifieddetected and rendered audible.

Power for supplying the necessary potentials for operating the various tubes is provided .by a power supply, not shown but which may also be conventional. However, the manner for supplying this power to the mixer and oscillator tubes is decidedly unconventional.

Considering first the mixer tube, which may be a 6SA7, this tube carries a high voltage on the screen grid, the voltage for this grid istaken from a line 20 whichalso furnishes power to .thescreen gr'd of the 6K7 radio frequency amplifying tube. Under normal conditions an ordinary filter would be considered suflicient if placed in the power supply lead to the mixer tube. lhis filter might comprise :a radio frequency choke to prevent R. F. current from getting into the line and a bypassing condenser for by-passing these indirect frequencies to ground. In this instance, however, it was determined that radio frequency was not sufficiently suppressed. It was then discovered that removing the choke .22 ,from the compar-tment 8 and placing it in a separate container 23 on the outside of the compartment 8, resulted in a materially greater suppression of the currents and that still greater effectiveness was realized if the choke was disposed in a shielded container supported on the outside of the compartment .5, while the by-pass condenser 24 is disposed and is grounded inside of thecompartment at 25.

In the case of the oscillator circuit, the plate voltage of the 6J5 which may be taken from the same high potential line, passes through a choke 25 from the line 20 and this choke is also disposed in a separate shielded container 25 on the outside of the compartment 5. In this instance as in the previous case, the by-pass condenser 21 is disposed in and grounded to the compartment 8.

The oscillator filament supply is also filtered ation is reduced to such a low level as to cause no interference. As an example, in a conventional receiver having a preselection in the radio frequency circuit, on the 9.6 m. c. to 1'5.6'm. c. hand, signals had previously measured 20 m. v. at the antenna of the receiver on 9.6 m. c. and when the receiver was tuned to 15.6 m. c. it had raised to 1000 m. v., but when the circuit was redesigned as described above, the raise was only m. v. It should also be noticed that whereas preselection in the R. F. section of a receiver has always been though to be the solution to this problem, it was'found to have very little, if any, effect at the higher frequencies, and that by this system of isolation of circuits it has been possible to reduce the radiation from a receiver to a point heretofore thought impossible.

Having thus described my invention, I am aware that numerous and extensive departures may be made therefrom without departing from the spirit of my invention.

I claim:

1. A superheterodyne radio receiver including a chassis base, a compartment completely shielded from said base and supported thereby and containing the antenna circuit components for said receiver, a second completely shielded compartment supported by, but electrically isolated from said base and containing the mixer and oscillator components for said receiver, a radio frequency circuit for said receiver said compartments, however, being electrically connected to said. base at predetermined points including said antenna circuit, and a vacuum tube amplifier having a base and a grid cap, said vacuum tube being completely shielded and having the base disposed in the mixer-oscillator compartment with the body of the tube bridging the space be tween the antenna and mixer-oscillator compartments and having the grid cap end extending into the antenna compartment, said mixer and oscillator sections including vacuum tube devices therefor, power supply means for supplying operating current to said devices, leads connecting the power supply to said mixer and oscillator sections means to prevent radiation from the mixer oscillator stages of said receiver comprising a filter disposed in the mixer screen voltage supply lead, said filter being disposed outside of the mixer oscillator compartment and completely shielded, a second filter disposed in the voltage supply lead to the oscillator and being outside of said compartment and completely shielded, and a third filter being disposed in the filament supply lead to said oscillator and disposed outside or said compartment and completely shielded.

2. A radio receiver of the class described, a chassis base therefor, an antenna circuit including tuning condensers and inductances and a shielded container for said antenna circuit, said container being supported in said base and electrically isolated therefrom said container however being electrically connected to said base at predetermined points; an oscillator and mixer circuit and vacuum tube device therefor, and a shielding container for said oscillator and mixer circuits supported in said base and electrically isolated therefrom; a vacuum tube device for said antenna circuit including a base and a grid cap, said tube having the base disposed in said last mentioned container and having the grid capextending into the first mentioned container and connected to the antenna circuit.

3. A radio receiver of the class described, a chassis base therefor, an antenna circuit including tuning condensersland inductances and a shielded container for said antenna circuit, said container being supported in said base and electrically isolated therefrom; an oscillator and mixer circuit and vacuum tube devices therefor, and a shielding container for said oscillator and mixer circuits supported in said base and electrically isolated therefrom said containers, however, being electrically connected to said base at predetermined points; a vacuum tube device for said antenna circuit including a base and a grid cap and having the base disposed in said last mentioned container and having the'grid cap extending into the first mentioned container and connected to the antenna circuit, power supply means including connecting leads for supplying operating voltages to said circuits and means to prevent radiation from the oscillator being coupled to the antenna circuit including radio frequenoy filters disposed in the power supply leads to the oscillator and mixer.

4. A radio receiver of the class described, a chassis base therefor, an antenna circuit including tuning condensers and inductances and a shielded container for said antenna circuit, said container being supported in said base and electrically isolated therefrom but being electrically connected to said base at a predetermined point; an oscillator and mixer circuit and vacuum tube device therefor, and a shielding container for said oscillator and mixer circuits supported in said base and electrically isolated therefrom; a vacuum tube device for said antenna circuit including a grid and having the grid connected to the antenna circuit, power supply means for supplying operating voltages to said circuits including plate, screen grid and filament supply leads, and means to prevent radiation from the oscillator being coupled to the antenna circuit including radio frequency filters disposed in the plate and filament supply leads to the oscillator and to the screen grid of the mixer.

5. A radio receiver of the class described, a chassis base therefor, an antenna circuit including tuning condensers and inductances and a shielded container for said antenna circuit, said container being supported in said base and electrically isolated therefrom said containers, however, being electrically connected to said base at predetermined points; an oscillator and mixer circuit and vacuum tube device therefor, and a shielding container for said oscillator and mixer circuits supported in said base and electrically isolated therefrom; a vacuum tube device for said antenna circuit including a base and a grid connection and having the base disposed in said last mentioned container and having the grid connection extending into the first mentioned container and connected to the antenna circuit, power supply means for supplying operating voltages to said circuits including plate, filament and screen grid supply leads, and means to prevent radiation from the oscillator being coupled to the antenna circuit including radio frequency filters disposed in the plate and filament supply leads to the oscillator and to the screen grid of the mixer, said filters including an inductance and a capacity, said inductance being disposed in a separate shielded container outside of the other containers.

6. A radio receiver of the class described, a chassis base therefor, an antenna circuit including tuning condensers and inductances and a shielded container for said antenna circuit, said container being supported in said base and electrically isolated therefrom said containers, however, being electrically connected to said base at predetermined points; an oscillator and mixer circuit and vacuum tube devices therefor, and a shielding container for said oscillator and mixer circuits supported in said base and electrically isolated therefrom; a vacuum tube device forsaid antenna circuit'connected to the antenna circuit including plate, filament and screen :grid supply leads, power supply meansfor supplying operating voltages to said circuits and means to prevent radiation from the oscillator being coupled to the antenna circuit including radio frequency filters disposed in the plate and filament supply leads to the oscillator and to the screen grid of the mixer, said filters including-an inductance and a capacity, said inductance being disposed in a separate shielded container outside of the other containers, and said capacitances being disposed inside of the second mentioned container and grounding thereto.

7. A radio receiver including a mixer circuit and an oscillator circuit each having a vacuum tube connected therein and each contained in separate shielded compartments, a power supply for supplying operating voltages to said tubes, said oscillator including an anode and a cathode, an anode line connecting the power supply to the oscillator anode, means to suppress undesired oscillations from said oscillator circuit including a filter in the anode supply comprising a capacity disposed inside of the oscillator compartment and bypassing said anode line to ground, and a choke disposed in the anode line and in a separate shielding container dispose outside of said compartment.

8. A radio receiver including an antenna circuit, a mixer circuit, and an oscillator circuit each having a vacuum tube connected therein and each contained in separate shielded compartments, a power supply means for supplying operating voltages to said tubes, said tubes including anodes and cathodes, anode and cathode supply lines connecting the power supply to said tubes, means to suppress undesired oscillations from said oscillator circuit including filters in the anode and cathode supply lines each comprising a capacity disposed inside of each compartment and bypassing said anode and cathode lines to ground and chokes disposed in the anode and cathode lines and positioned in separate shielding containers disposed outside of said compartments.

9. A radio receiver of the class described, a chassis base therefor, an antenna circuit including tuning condensers and inductances and a shielded container for said antenna circuit, an oscillator and mixer circuit and Vacuum tube devices therefor, and a shielding container for said oscillator and mixer circuits, a vacuum tubedevice for said antenna circuitconnected to the antenna circuit, power supply means for supplyingoperating voltages to said circuits including plate and filament supply leads connected to the oscillator and a screen grid supply lead connected to the mixer, and means to prevent radiation from the oscillator being coupled to the antenna circuit including radio frequency filters disposed in the plate and filament supply leads to the oscillator and to the screen grid of the mixer, said filters including an inductance and a capacity, a separate shielded container outside of the other containers said inductance being disposed in separate shielded container, and said capacitances being disposed inside of the second mentioned container and grounded thereto.

10. A superheterodyne radio receiver including a chassis base, a shielded compartment electrically isolated from said base and supported thereby and containing the antenna circuit components for said receiver including the tuning controls, a second completely shielded compartment supported by but electrically isolated from said base and containing the mixer and oscillator components for said receiver including an oscillator tuning control; an insulated coupling mechanically connecting the antenna tuning control to the oscillator tuning control, said compartment however being electrically connected to the chassis base at predetermined points, a radio frequency circuit for said receiver including said antenna circuit, and a vacuum tube amplifier, said vacuum tube being completely shielded and including a base and a grid cap and having the base disposed in the mixer-oscillator compartment with the body of the tube bridging the space between the antenna and mixer-oscillator compartments and having the grid cap and extending into the antenna compartment, said mixerand oscillator sections including vacuum tube devices therefor, power supply means for supplying operating current to said devices, and connecting leads for connecting said power supply to said devices including a mixer screen voltage supply lead, an oscillator voltage supply lead and a filament supply lead means to prevent radiation from the mixer oscillator stages of said receiver comprising afilter disposed in the mixer screen voltage supply lead, said filter being disposed outside ,of the mixer oscillator compartment and completely shielded, a second filter disposed in the voltage supply lead to the oscillator and being outside of said compartment and completely shielded, and a third filter being di. posed in the filament supply lead to said oscillator and disposed outside of said compartment and completely shielded.

MARVIN HQBBS.

Patent No. 2,51%569.

CERTIFICATE OF CORRECTION.

March 16, 19M.

MARVIN HOBBS.

It is hereby certified that error appears in the printed specification I of the above numbered patent requiring correction as follows: Page 1, second column, line 2 9,'for the Word "carry" read carryingpage 5, first column, line 5, for "though" read -th'ought-; line 25, claim 1, after "receiver," insert said compartments, however, being electrically connected to said base at-predetermined points,-; lines 24., 25 and 26, same claim, strike out "said compartments however, being electrically connected to said base at predetermined points"; page 1;, first column, lines 5 and h claim 6, I

strike out including plat filament and screen grid supply leads"; line 5, same claim, after "circuits" insert -including plate, filament and.

screen grid supply leads,-; and second column, line 11, claim 9, after "in" insert the and that the said Letters Patent should be read with this correction therein that the same may conform toithe record of the case in the Patent Office. I

Signed and sealed this llth day of May, A. D. 915

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

